Variable speed correction for automatic pilots



' Oct. 24, 1939. F G, NESBHT 2,176,922

VARIABLE SPEED CORRECTION FOR- AUTOMATIC PILOTS Filed June 16, 1937 2Sheets-Sheet l //Vl ENTOQ FwA/c/s 6. /I/4= 5/77- Oct. 24, 1939. F. G.NESBITT 2,176,922

VARIABLE SPEED CORRECTION FOR AUTOMATIC PILOTS Filed June 16, 1937 2Sheets-Sheet 2 5 /2a 2 /22 van 34 133 i r k 137 H6115 I FRA'A/c/s 6.4255/ 77' 4 r wave/1 Patented oct."24,.1939

VARIABLE SPEED CORRECTION FOR AUTOMATIC PILOTS r Francis G. Nesbitt,Dayton, Ohio Application June 16, 1937, Serial No. 148,559 15 Claims.(Cl. 244-76) (Grantednnder the act '01? March 3, 1883, as

amended April a0, 1928; 370 o. G. 757) The inventior. described hereinmay be manufactured and used by or for the Government for governmentalpurposes, without the payment to me of any royalty thereon.

When an experienced airman operates an airplane manually, he appliescorrections to the control surfaces at different rates depending on themagnitude of the disturbance and thereby obtains very smooth flight.That is, for very small corrections 'required to keep the airplane on apredetermined course and level, he moves the controls .very slowly. Whendisturbances or gusts and bumps are encountered, greater corrections:are required and they must be applied much more quickly in order toobtain maximum smoothness. The airman learns by experience andsubconsciously applies corrections faster for large disturbances,although the small corrections required to keep the airplane level andon course are applied very slowly.

In automatic pilots now being used, the speed of correction (i. e., thespeed at which the controlsurfaces .are moved) is a constant value. Thisconstant value ,is adjustable manually for different predeterminedconditions.

regards to flight smoothness. With correction speed manually set low forsmooth air, the

automatic pilot will not fly the airplane smoothly in disturbed airbecause the control surfaces-are not moved fast enough. When thecorrection speed is manually set high. for disturbed air, the controlsurfaces are moved so fast that the small corrections are applied veryrapidly, re-

sulting in extremely mechanical and unnecesresult is that presentautomatic pilots do not pro-. vide as smooth a flight as maybe obtainedby the human pilot except under very specific conditions which do notalways exist.

The purpose of my invention is to provide a simple means whereby anautomatic pilot will continuously apply corrections "very slowly to keepthe airplane on a predetermined course and Experience has shown,however, that there is much room for improvement with these automatic,pilots with level, and with the same setting apply corrections veryquickly, when required, to counteract periodic air disturbances or bumpsand gusts.

My invention produces a variable correction speed and is arranged sothat the minimum speed is obtained at and near the zero or neutralposition of the servo mechanism. As the servo mechanism departs from theneutral position in either direction, the correction speed isautomatically increased. Therefore, large corrections are produced morerapidly and small corrections are produced very slowly. The rate ofchangeof correction speed is adjustable in order to be useful onairplanes of different types.

Although my invention is primarily a device to improve the performanceof automatic pilots, it-should be understood that it is applicable toany automatic mechanism incorporating a servo unit. For example, thisvariable correction speed may be used to advantage in the relaymechanism which automatically sets the heading on an automatic pilot bythe signal received from a radiovcompass or homing device. Anotherexample would be use in connection with the automatic operation ofengine controls and/or propeller pitch controls.

In the description that follows, one servo unit only is shown. In anautomatic pilot, there are actually three .of these units, one each forthe aileron, the elevator and the rudder controls. This invention isillustrated in the following description by two methods; first, aspecial restriction valve or valves used in conjunction with anhydraulic type servo unit, and second, an arrangement using a rheostatinconjunction with an electric type servo unit. It should be understoodthat othr arrangements may be used Without departing from the spirit ofthe invention, such as pneumatic mechanisms, etc.

Referring to the drawings, in which numerals of like character designatesimilar parts throughout the several views Figure 1 is a schematicrepresentation of a well known form of hydraulically operated auto maticpilot;

Figure 2 represents fluid flow for left wing low correction; 1

Figure 3 represents fluid flow for right wing low correction;

Figure 4 is a side elevation, in partial crosssection, of one embodimentof any invention ap plied to the above automatic pilot;

Figure 5 is a perspective View of myvariable restriction valve;

Figure 6 shows partial disassembly of Figure 5 Figure 7 shows minormodification of. Figure 6;

and

Figure 3 shows a side elevation of a second embodiment of my inventionapplied to the above automatic pilot.

In the schematic representation of Figure 1, a gyro unit I (intendedonly for association'with the aileron controls of an aircraft) isoperably connected to a'control unit 2 governing fluid flow to aservo-unit 3. An inner gimbal, ring 4 of a rotor 5, is mounted to pivotabout an axis' Z,Z'

. normal to gyro axes Y-Y' and'X-X at their point of commonintersection. The axis XX' is intersected by two, spherically formedbaflle plates 6a and 6b, fixed to and rotating with the gimbal ring 4.The upper edges of the baffle plates 6a and 6b are arranged to partiallycover respectively, jet openings Ia and 1b provided in a second set ofspherically formed plates 8a and 8b, closely superimposed about theouter surfaces of the baffle plates 6a and 6b. The .plates 811 and 8bare pivoted as a single unit above axis Z Z by means of a pulley-9, ashaft I8 and a gear supported bya box |2. Air pickofls l3 and M are,flexibly connected to the jet openings la; and lb. A rotor jet -|5 isfixed to the box l2, as indicated, the gyro unit I being completed byinstallation of a suction regulator l6 and a suctionpump ll at the upperright hand portionof the box l2.

The control unit 2 is composed of an oil pump I8, an oil pressureregulator l9 operably connected to an oil sump 28 and a speed controlvalve 2|, a balanced oil valve 22, and an air relay 23. As shown inFigure 1, the pump |8 continues to by-pass through the oil sump 28. Thebalanced oil valve 22'is provided with an axially slidable valve 24, a.principal oil inlet 25 connected with the speed control valve 2|, oil

outlets 26 and 29 connected with the oil sump 28,

an oil pressure regulator 30. The air relay 23 is divided into separatechambers B and A by means of a central diaphragm 3|. Air is sucked intochamber A through a port 32 and from thence into the air pickofi. Air issucked into chamber B through a port 33 and from thence into the airpickoff l4. The centerof the diaphragm 3| is operably connected to theright extremity of the slidablevalve 24 by means of a connecting rod34..

I The servo-unit 3 consists of a motor 35 including a cylinder 36, apiston 31, a piston rod 38 and inlets-outlets 39 and 48; a by-pass 4|including a valve 42. with a pulley 43 fixed to the rotor thereof, acontrol handle 44 with a pulley 45 fixed to the base thereof, a cable 48lntercon necting pulleys 43-45 and a by-pas pipe 41;a restriction valve48 interconnected to the oil pressure regulator 30 and the inlet-outlet39 by means of pipes 490. and 49b; a restriction valve 58 interconnectedto the oil pressure regulator 30 and the inlet outlet 48 by means ofpipes 5|a and 5|b; a cable 52 adapted to be operably connected to theaileroncontrols of an aircraft; and a cable 42 and the pipe4'l are builtdirectly into the cyl- 53 passing over pulleys 54 and operably connectedwith'the pulley 9 of the gyro unit I.

In the description of the operation of the three unitsof Figures 1, 2,and 3, the restriction valves 48 and 50 are first considered ascompletely removed from the figures in order that the operation ofautomatic pilots existing pridr to my invention may be clearlyunderstood; i. e, inlets-outlets 39 and 40 of the servo-unit 3 aredescribed as directly connected to the oil pressure regulator 38 of thecontrol unit2.- The efcombined longitudinal axes of wing panels 55a and55b, as well as the axis X-X' of the rotor 5,, are being maintainedcoincidental (as viewed from the propeller end of the aircraft). Duringcontinuation of such wing attitude, the suction pump exhausts relativelyequal volumes of air from chambers A and B of the air relay 23 (through,respectively, air pickoffs l3 and I4 and the equally partially coveredjet openings la and lb). The diaphragm 3| and the slidable valve 24remain in the central positions shown in Fig. 1 such that no oil will bedischarged from the oil pressure regulator 38 to the cylinder servo unit3.

Let it be assumed that disturbed air causes wing panel 55b to fall belowtrue horizontal (a condition known to the art as left wing lowpilotsviewpoint). counterclockwise rotation of the baffie plate 6b from theparts showing of Figure 1 causes momentary coverage of the jet opening1b, whereupon the diaphragm 2| and the slidable valve 24 of the controlunit 2 assume the positionings of Fig. 2. Fluid from the oil pressureregulator 38 thereupon commences to flow-through the inlet-outlet 48 ofthe motor 35, causing thepiston rod 38 andthe cable 52 attached theretoto move to the left of the parts showing of Figure 1, such that theaileron of wing panel 551) is depressed and the aileron of wing panel55a is elevated. In order that over-controlling of the ailerons may beprevented, as soon as the piston rod 38 moves 36' of the' of the gyrounit I executes a clockwise movement,

causing an immediate counter-clockwise movement of the plates 8a and 8b.Through combination of the-aforesaid parts movements, the wing panel 55bis restored to normal lateral attitude.

If disturbed air causes right wing low attitude of the aforesaid wingpanels, the diaphragm diately followed by clockwise movements of theplates8a and 8b. Through combination of the aforesaid parts movements,the wing panel 55a is restored to "a normal lateral attitude. Duringtake-01f and landing of an aircraft, it may prove desirable for thepilot to retain manual control of the aforesaid ailerons. Such controlis assured by counterclockwise rotation of the control handle 44 intotrue horizontal, thereby by-passing the piston 31 with respect to theinlets-outlets 39 and 48 of the servo unit 3. Y

In Figure 4, I show the detailed, structure of the servo unit 3. It willbe noted that the valve with an enlarged central threaded portion 58,

upon which are assembled a piston leather 59,

piston washers 68, check nuts 5|, and cotter pin 62. The two open endsof the cylinder 36 are provided with cylinder headers 63, fixed theretosure regulator 30 of the control unit 2 are di- 16 secured to thestructure H by means of bearrectly connected to the inlet openings ofrestriction valves 48 and 50. The outlet openings of the restrictionvalves 48 and 50 are thereafter directly connected with the passages 56and 51 by means of a pipe 49b, a pipe 5Ib and pipe connections 61. Therestriction valves 48 and 50 are provided respectively with forkedlevers 68a and 68b radially adjustable as described in Figure 5. It willbe further noted that both of the aforesaid valves are cradled in bases69, provided with hinged straps 10, and that they are laterallyadjustably secured to asupporting structure 1I by means of screws 12passing through longitudinally slotted openings 13 provided in the bases69.

Referring again to Figure 4, the piston rod 38 is provided at its outertwo extremities with detachable driving pins-14a and 14!), adapted toremain in constant engagement with the inner surfaces of the forkedlevers 68a and 68b. The tip extremities of the piston rod 38 are alsoprovided with openings 15a and 15b to which are secured the inner endsof the cable 52. The cable 53 is spliced tothecable 52,asindicated.Thesideportions of the cable 52 are supported by pulleys ing pins 11,the upper mid-portion thereof being fixed to openings 18a, and 1812provided in a sliding plate 19. The sliding plate 19 moves laterally inguide plates fixed to the structure II and is further provided with adriven pin 8| at its central portion. The driven pin 9| is adapted to bein constant engagement with the inner surfaces of a forked lever 82. Theforked lever 82 is provided with openings 83a and 83b to which are fixedaileron control cables 84, 85, 86 and 81a and with a mounting boss 88,which is. rotatably secured to the structure H by means of a bearingshaft 89. The right hand end of the cable 81a is fixed to a pilotsaileron control stick 90, from the right side of which further continuesaileron cable 811).. Manual control ofthe ailerons cannot be utilizeduntil the pilot aligns the central opening in the valve 42 (of the motorwith the by-pass opening 41' provided between passages 56 and 51 of thehousing 36, through rotation of the control handle 44 fixed to an outerend of the valve 42.

Figure 5 shows an enlargement of the restriction valve 48. The interiorof the valve is provided with a valve rotor. 9| from which projects adriving shaft 92. The aforesaid parts are encased in a top housing 93and a bottom housing 94, secured in assembled relationship by means.

on the outer surface of the former, while similar angular adjustment ofthe restriction valve 48, with reference to the structure H, andtherefore alignment with the longitudinal axis of the piston rod 92 isaccomplished by means of further numeraled graduations IOI provided onthe outer surface of the top housing 93.

Referring jointly to Figures 5 and 6,'it will be noted that thebottom'housing 94 is provided with inlet and outlet cavities I02 and I03which are in direct communication, respectively, with the pipes 49a and49b, fixed to the rear surface of the aforesaid housing by" means ofpipe connections. The inlet cavity I02 is provided with a metering blockI04, fixedly secured by means-of pins I05.

It will be noted that the metering block I04 15 left. hand extremity ofthe cylindrical opening] I06 may be varied at will, whereas in thearrangement Figure 6, the metering block I04 must be replaced to makethis adjustment. The arrangement shown in Figure 7 will also permit theuse of interchangeable metering screws I09 with different end profileswithout the necessity for dismantling the valve assembly.

The first variable. correctionspeed embodiment of my invention operatesas follows: With the piston 31 in the neutral position, the aileroncontrol surfaces are in neutral position, and the cylindrical openingI06 is symmetrically restricted by metering block I04 as shown in Figure6. When very small corrections are required of the automatic pilot inorder to maintain level attitude the flow of the incoming fluid is.restricted by the presence of meterin'g block I04. As the piston rod 38moves a small amount for small corrections, the cylindrical opening I06of the restriction valve 48 also moves a small amount relative to blockI04. Therefore, the fluid flow is still appreciably restricted and thecorrection is applied slowly. When larger corrections are required tocounteract air disturbances or bumps and gusts, the cylindrical openingI06 of the restriction valve 48 moves farther away from the neutralposition of the block I04 and opening I06. The farther the opening I06travels from block I04, the less the restriction to the fluid flowbecomes, due 'to the design of the metering block I04 shown in Figure 6or the metering screw I09 shown in Figure 7. Therefore, for largecorrections, since the restriction to flow of fluid becomes very muchless, the speed of correction is greater. It is obvious that the actionjust described is obtained for either direction of movement fromneutral. The action of restriction valve 50 is identical with that ofthe restriction valve 68, just'described, and both of these valves arearranged to provide simultaneous restrictions to fluid coming in oneside of the cylinder 36 and fluid going from the other side of cylinder36 of the motor 35. It may be sufficient in connection with someinstallations to use only one valve; that is; the restriction valve 59may be omitted and pipes Sid and 5H) consolidated into a single pipe 5i,directly connecting the inlet-outlet 39 operably connected at its righthand extremity In Figure 8, I show a second embodiment. of my inventionwherein, a servo unit I I0, consisting of an electric motor III and acontroller 2, is

to a control unit H3 and at its left hand extremity to a' cablepulley-rheostat assembly -I I4. It will be noted that the control unitH3 consists solely of the air relay 23, no necessity existing forinclusion of the pump I8, the regulator IS, the sump 20, or the valves2| and 22 of Figure 1. The cable pulley-rheostat assembly III is drivenby the motor III through a shaft 5 and worm gears III; and III. A cableIIIl is fixed at any suitable point to the outer surface of a pulleyII19 forming an inner portion of the assembly III. The cable II8duplicates the function performed by the cable 52 of Figure 4, its uppercentral portion being fixed to openings 18a and b of the sliding plate19. The'cable 53 is spliced to the cable II8, as indicated. The assemblyIII is provided with a contactor arm I20, adapted to sweep in anarcuatepath over rheostat segments I2Ia and I2 lb. The plate portion of thecontactor arm I20.is electrically connected to a lead wire I22 of one ofthe rotor coils encased within the motor III, while the remaining leadwire I23 of the other of the aforesaid rotor coils is electricallyconnected to the outer plate of a bi-plated contactor arm I24 of'thecontroller II2. Alead wire I25 of one of the stator coils of the motor,I I I is connected to an outer contactor segment I26 by means of a wireI21, while the remaining lead wire I28 of the aforesaid stator coils, isconnected to an inner contactor segment I29 by means of a wire I30. Itwill be noted that the first lead wire I25 is further connected to aninner contactor segment I3I by means of a wire I32, while the secondlead wire I28 is further commonly connected to an outer contactorsegment I33 by means of a wire I34. The inner plate of the contactor armI24 is electrically connected to one pole of a direct current source I35by means of a wire I36. The other pole of the. current source I35 isjointly connected to the two outer extremities-of the rheostat segmentsI2Ia and I 2") by means of wires I31 and I38, respectively. Returningtothe contactor arm I24, that portion thereof extending to the right ofjournal pin I319 v for the above through the control unit I I3 (airrelay 23), the servo unit I I 0 and the cable pulleyrheostat assemblyIll; .i. e., reversing currents are caused to flow through the motor I II, induced by clockwise or counter-clockwise rotation of the contactor'arm I24. Heretofore there was no secondary means for reducing initialflow to a minimum. In this second embodiment of my invention, I retardcurrent flow brought about by reaction to small corrections throughintroduction of the rheostat segments I2Ia and I2Ib and the contactorarm I20, between one pole of my direct current source I35 and the leadwire I22 to one of the rotor coils of the motor III. For, largercorrections, as the contactor arm I20 approaches an outer end of eitherthe rheostat segment I2Ia or I2Ib,' the current flow increases; and therotation of the motor I I I is speeded up".

Although the description is specific to the illustrations in thedrawings, it is to be understood that there may be numerous departurestherefrom which will still be within the field and scope of myinvention, so that I do not wish to be restricted thereto, but onlyinsofar as .the appended claims are so limited.

What I claim is:

1. In an automatic pilot for aircraft, the combination with referenceresponsive means for maintaining a predetermined flight condition, acontrol surface, a servo motor controlled by said means for operatingsaid surface and a follow-up connection between said servo motor andsaid reference means; of additional means included in said follow-upconnection and operated by said servo motor for regulating the controlof the servo motor by said reference responsive means insuch a mannerthat the speed of movement of said servo motor varies in predeterminedrelation to a predetermined change in the relation of said aircraft tosaid reference responsive means.

2. In an automatic control system, the combination with a source offluid pressure, a fluid with said valve means and source and operable inresponse to the movement of said part for varying the .rate of the powersupply .as a function of a predetermined change in the condition of saidreference means and thereby obtain a predetermined variation in thespeed of said power operated part, said variation 'being separate fromand in addition to the control obtained by said valve means.

3..In an automatic pilot for aircraft, the combination with gyroscopicresponsive fluid operated means for maintaining a predetermined flightcondition, a control surface, a servo motor controlled by said means foroperating said surface and a follow-up connection between said servomotor and said gyroscopic means; of fluid metering means additionallyincluded in said followup connection and operated by said servo motorfor regulating the control of the servo motor by 'said gyroscopic meansin such a mannerthat the speed of movement of said servo motor varies inpredetermined relation to a predetermined change in the relation of saidaircraft to said gyroscopic means.

4. In an automatic control system, the combination with a source ofpower, a power operated part movable in either of two directions from aneutral position, means controlling the actuation of said part and areference means for automatically controlling said first controllingmeans I to regulate the supplyof power for operating said part, meanscontrolling the actuation of said part and a reference means forautomatically controlling said first controlling means to regu-2,176,922 late the supply of power for operating said part of means inseries with said source and said first controlling means and operable inresponse to the movement of said part for obtaining a predeservo-motorfor operating said surface in eitherand servo-motor and havingcommunication with the liquid inlet and the liquid outlet of saidservomotor and connected to said servo-motor to be operated thereby soas to vary the speed of operarestriction progressively decreasing as therotor is 5 termined increase in the speed of movement of tion of saidservo-motor in either direction from 5 said part for each increasingchange in the maga neutral position corresponding to the neutral nitudeof said movement, said increase being position of said surface in apredetermined separate from the control obtained by said other manner.controlling means. 11. In an automatic pilot for aircraft, the com- 6.In an automatic pilot for aircraft, the com- 'bination with a controlsurface, an electrically 10 bination with a reference responsive meansfor operated servo-motor for operating said surface maintaining adesired flight condition, a control in either direction from a neutralposition and surface, a servo motor controlled by said means electricalmeans controlling said servo-motor, of for operating said surface and afollow-up conresistance means in addition to said first con- 1 nectionbetween said servo motor and said refertrolling means and operated bysaid servo-motor ence means; of additional means included in said tovary the speed of operation of said servofollow-up connection andoperated by said servo motor in either direction from a neutral positionmotor for regulating the control of the servo corresponding to theneutral position ofsaid surmotor in such a manner that the speed ofmoveface in a predetermined manner,

ment of said servo motor varies in predeter- 12. In an automatic pilotfor aircraft, the comgr mined relation to a predetermined change in thebination with a control surface and an electricalrelation of saidaircraft to said reference means. ly operated servo-motor for operatingsaid sur- 7, In an apparatus having a part to be operated face in eitherdirection from a neutral position,

- by a source of electrical power in either of two of adjustable res s ace ea s p t y Said directions from a neutral position and a givenservo-motor to progressively increase the speed 25 reference means forcontrolling the supply of of operation of said servo-motor in eitherdirecpower, electrical means responsive to themovetion from a neutralposition corresponding to meat of said part to increase the rate ofapplicathe neutral position of said surface in a predetertion of poweras a function of a departure of said m ned ma ner- I 20 part fromaneutral positionineither direction to 3- in a flui est ct Valve C pr aw obtain a progressively increasing speed of said housing, having twofluid cavities, a rotor operpart in either direction as it departs fromneutral. ating therein and hav a Opening in communi- 8. In an automaticcontrol system, the comb-ication with said cavities, a convex meteringblock nation with a source of power, means adapted to disposed in one ofsaid cavities and being so ar- 36 be actuated by said source of powerincluding a ranged that the maximum restriction to fiuldfiow servo-motorand a member operated thereby, through the opening is obtained when therotor nieans controlling the actuation of said servois inthe neutral orsymmetrical position, said remotor and a given reference means forcontrolling striction progressively decreasing as the rotor is saidfirst controlling means to regulate said power turned in eitherdirection from said neutral or no supply, of means in series with saidsource of central position.-

' power. and said first controlling means for regu- 14;. In a fluidrestriction valve, comprising a lating said power supplyifor obtaining apredehousing, having two fluid cavities, a rotor operterminedvariationin the speed of movement of atlng therein and having an opening incommunisaid member to the variation in the magnitude cation with saidcavities, an adjustable metering g of said movement, said regulationbeing separate screw disposed in one of said cavities and being as fromthe control obtained by said other controlso constructed and arrangedthat the mammum llng means, restriction to fluid flow through theopening is oh- 9, In an apparatus having a part to be opertained whenthe rotor is in the neutral or symated by a source of electrical powerin either of metrical position, said restriction progressively a twodirections from a neutral position and a decreasing as the rotor isturned in either direc to" yglven reference means for controlling thesupply tion from said neutral or central position.

of power, variable electrical means responsive to \15. In a fluidrestriction valve, comprising a the movement of said part to increasethe rate of housing, having two fluid cavities, a rotor operapplicationof power as a function of a departure ating therein and havin an openingin communig of said part from a neutral position in either dication withsaid cavities, a readily removable, ad- 5 rection as it departs fromneutral, and means justable metering screw disposed in one of said forsetting said variable speed means for obtaincavities and being soconstructed and arranged ing minimum speed at the neutral position. thatthe maximum restriction to fluid flow i 10: In an automatic pilot foraircraft, the comthrough the opening is obtained when the 'rotor Ibination with a control surface, an hydraulic is in the neutral orsymmetrical position, said direction i'roma'neutral position and valvemeans turned in either direction from said neutral or for controllingthe actuation of said servo-motor, central position. I of metering meansin series with said valve means G. NESB

